Spectral emission coding



Nov. 26, 1968 J. w. BERRY SPECTRAL EMISSION CODING Filed Feb. 9, 1966INVENTOR. JOHN W/LL/AM BERRY ATTORNEY United States Patent M 3,413,481SPECTRAL EMISSION CODING John William Berry, Stamford, Conn., assignorto American Cyanamid Company, Stamford, Conn., a corporation of MaineFiled Feb. 9, 1966, Ser. No. 526,191 5 Claims. (Cl. 250--226) ABSTRACTOF THE DISCLOSURE Coded symbols are produced, the coding representingpresence or absence of metals having sharp emission lines under sparkdischarge. The symbols, on a suitable substrate, are read out by passingeach symbol through a spark discharge at a repetitive rate of sparks,detecting the sharp lines in a plurality of detectors, one for eachmetal, and sending the signals from the detectors through readoutcircuits responding to the presence or absence of the coded components.The detectors may be photomultiplier tubes or solid state detectors withlimitations to the line to be detected, for example, sharp cuttinginterference filters. Preferably the light from the spark discharge isled to the detectors by fiber optics to permit a wider physicalseparation of detectors.

Background of the invention In the co-pending application of Freeman andHalverson, Ser. No. 596,366, filed Oct. 14, 1966, which is acontinuation-in-part of an application Ser. No. 437,866, filed Mar. 8,1965, now abandoned, both applications being assigned to the assignee ofthe present application, there is described a process for encoding andretrieving information by means of coded inks containing variouscombinations of components which fiuoresce under ultraviolet or shortwave illumination at different wavelengths. Preferably there areincluded for at least some of the components chelated lanthanide ionswhich fiuoresce in very narrow bands. Coding can be in terms of presenceor absence of particular components, and this permits a number ofsymbols equal to 2 -1 Where n is the number of components. For example,four components permit fifteen different symbols, six components 63, andthe like. The coded symbols have the advantage that they do not dependon the shape of the symbol as is needed in other systems, for examplebank check account numbers in magnetic inks and the like.

A problem is presented in the number of components Summary of theinvention The present invention eliminates the problems of symbol numberby using metals or metal compounds and reading out the coded inks orother symbol forms by subjecting the symbols to a spark dischargeproducing the spark spectra of the metal components present anddetecting sharp lines which are unique for the particular components.The number of metals which are practical is very much greater than thenumber of photoluminescent materials available with the sharpfluorescent bands, and this is one of the principal advantages of thepresent invention, although for certain particular uses, such aspersonal identification and the like, the invention presents otheradvantages.

While, theoretically, it might be thought that any metal 3,413,481Patented Nov. 26, 1968 could be present as a component in the codedsymbols, as a matter of practical use the choice is somewhat morelimited though the number of components is greater than with practicalphotoluminescent materials. Certain metals are not suitbale because ofthe enormous number of closely adjacent lines; typical examples of suchmetals are the transition metals, iron, nickel and cobalt. Other metals,such as for example silicon, sodium, potassium and the like, while theyhave reasonably intense lines sufficiently separated, are unsuitablebecause many substrates, such as for example paper, on which the codedsymbols may be formed, are apt to contain such materials as impuritiesor as deliberately added components, for example, siliceous fillers inpaper and the like. This leaves as the preferred metals bismuth,gallium, germanium, lithium, cadmium, lead, scandium, silver, mercury,tin, zinc and zirconium. It should be understood that the invention isnot strictly limited in its broader aspects to these preferred metalcomponents, because with a little care, for example in the choice of asubstrate, it is possible to use some of the other metals, thelimitation only being that they shall have strong lines sufficientlyseparated from other lines of other components to permit spectralseparation and detection. In a more specific aspect, however, thepresent invention contains the limitation to the preferred metals setout above.

The form in which the metal components are mixed to produce the codingand applied to substrates or formed into symbols presents no problem.For example, inks may be made of solutions or dispersions of metalsalts, always taking care that the anion of the salt does not itselfemit lines on spark excitation which would be overlapping and henceconfusing with the metal itself or with the metals of other components.It is also possible to precipitate relatively insoluble metal compoundsor the metal itself on substrates. This is particularly readily effectedwith metals such as silver which can be transformed into the metallicstate by exposure to light. Where there is no objection to visibleevidence of the presence of particular components, this makes silver avery useful metal for one of the cornponents. It should be noted that inthe present invention, just as with the photoluminescent coded inks ofthe Freeman and Halverson applications, it is sometimes desirable thatthe coded message be secret, that is to say that the symbols in thecoded inks be colorless. For other uses, such as for example accountnumbers on the edge of bank checks, there is an advantage in having thesymbols visible, which can easily be effected by including a suitablepigment. In such cases, the account number can be read either visually,if there has been no mutilation of the shape of some of the symbols, orby machine reading using spark excitation.

The present invention also permits a different physical form because themetals for the most part can be alloyed, and thus relatively strong andpermanent articles can be produced, such as a rod, a metallic coating ona plastic identification card, and the like. When such an identificationobject is inserted in the reader at a plant gate or gnards desk, thereadout will confirm the identity of the owner. Obviously of course thechoice of metals for alloying are subject to some limitation, forexample they must be capable of forming alloys and the alloys should bereasonably non-cornoding, thus for example lithium and mercury are lesssuitable for this last use than some of the other metals.

The nature of the readout mechanism for determining the presence of theparticular metals can be quite varied, and the present invention is notlimited. to any particular type of readout. Thus, for example, forreadout machines which are permanent and adapted to read fairly lowconcentrations of the components in the coded symbols, photo-multipliertubes as detectors present many advantages. Thus they are extremelyfast, extraordinarily sensitive, and so even when used with extremelysharp cutting filters, such as for example low transmission interferencefilters, adequate signals are produced. On the other hand, where thereadout is simpler and where space, portability or cost are moreimportant, solid state radiation detectors, such as cadmium sulfide,lead sulfide and the like, may be preferred. Because of the lowersensitivity it will often be necessary to associate such detectors withpreamplifiers or other electronic circuits which increase the signal tothe desired level. Time constants of the detectors are also notnecessarily without significance. Where very fast reading of symbols isrequired, short time constant detectors are of course needed, and thisis another case where the high sensitivity photo-multiplier tubes havevery advantageous characteristics. However, for identification machineswhere speed of reading is of little or no importance, the cheaper, morecompact, and lower voltage devices, such as solid state detectors, maybe preferred in spite of the fact that they have somewhat longer timeconstants, particularly at low signal levels, which makes them lesssuitable for extremely high speed reading. All in all, it is anadvantage of the present invention that a wide range of detectors may beused so that the best combination of characteristics for any particularuse may be chosen.

Spark production from conventional sources, such as Tesla coils, usuallyproduce a series of sparks at very short repetition intervals. Theresulting signals from the radiation detector are therefore suitable foramplification and other processing in AC electronic circuits which havemany advantages, such as freedom from drift and the like. Of course thecircuits used and the detectors must be suitable for the repetition rateof the sparks used in reading the coded information.

Brief description of the drawing The drawing is an isometric view of areadout apparatus.

Description of the preferred embodiments The invention will be describedin greater detail in conjunction with the drawing, which illustrates, insemidiagrammatic form, a typical readout mechanism for six componentcoded symbols. A metallic table 1 is provided across which a codedobject 2 such as a car-d or bank check is moved. At 3 an aluminumelectrode extends in close proximity to the surface of the card.Repetitive spark discharges are produced by conventional spark dischargesupply 4 shown as connected to the electrode and to the table by wires 5and 6. Sparks are produced at a predetermined repetitive rate, and theradiation from the discharge is led through fiber optics light pipes 7to six detectors. These detectors contain photomultiplier tubes andsharp cutting interference filters, and are labelled clockwise Zn forthe 6362.3 A. line, Ag for the 328068 A. line of silver, In for the4101.77 A. of indium, Ge for the 3039.06 A. of germanium, Ga for the4172.06 A. of gallium, and Cd for the 6438.47 A. line of cadmium. Thedetectors are connected by wires (not numbered), to an electronicreadout 8, which is shown diagrammatically as the circuits areconventional binary to digital conversion circuits.

Mention has been made of an aluminum electrode bebecause aluminum doesnot have strong emission lines in the visible, although it does havestrong emission lines in the ultraviolet, which of course are easilyeliminated from the detectors by the sharp cutting filters. Anothermetal which can be used for the electrode is lead, which also has mostof its strong lines in the ultraviolet. Since we are concerned with thesurface of the electrode which is in contact with the spark, it is ofcourse perfectly possible to have a coating of lead or aluminum onanother metal for the main electrode body.

I claim:

1. A coded ink symbol printing and information retrieval system usingcoded inks having metallic components and a readout mechanism comprisingin combination,

(a) two electrodes with space therebetween for receiving an article withcoded symbols,

(b) means for producing a series of sparks between the electrodes andthrough the coded symbols at a predetermined repetition rate,

(c) radiation detectors for the different metal components respondingsharply only to a preselected strong line in the spark emission spectrumof each components, said detectors transforming radiation intoelectrical signals, and

((1) electronic means actuated by the signals from the detectors forreading out coded symbols.

2. A system according to claim 1 in which the detectors arephotomultiplier tubes with sharp cutting filters.

3. A system according to claim 1 in which radiation detectors are solidstate detectors with sharp cutting filters.

4. A system according to claim 1 in which the metals comprise aplurality of metals selected from the group consisting of bismuth,cadmium, lithium, gallium, germanium, indium, lead, mercury, silver,tin, zinc, and zirconium.

5. A system according to claim 2 in which the metals comprise aplurality of metals selected from the group consisting of bismuth,cadmium, lithium, gallium, germanium, indium, lead, mercury, silver,tin, zinc and zirconium.

References Cited UNITED STATES PATENTS 2,577,814 12/1951 Saunderson etal. 250-226 X 2,823,577 2/1958 Machler 8814 2,951,164 8/1960 Timms 25071X 3,144,551 8/1964 Webb et al 88--14 X ARCHIE R. BORCHELT, PrimaryExaminer.

